Anyway, I've tried to solve this problem by myself, but unfortunately I've got the same logic expression so I couldn't simplify my logic expression using that method...I was some confused about simplifying such logic ABC'+A'B'D as each term consists of three variables of four , I have no problem with simplifying logic expression such as ABCD'+A'B'CD as each term consists of four variables of four... hope that I could explain my problem... my problem is not with understanding the method in general !
thanks a lot!
Another thing, i want to apologize for the wrong post in wrong section...i'm sorry!
best regards!